Nonfactorizable charming-loop contribution to FCNC $B_s→ γ l^+l^-$ decay

We present the first theoretical calculation of nonfactorizable charm-quark loop contributions to the Bₛ→ γ l⁺l⁻ amplitude. We calculate the relevant form factors, HA,VNF(k'²,k²), and provide convenient parametrizations of our results in the form of fit functions of two variables, k'² and k², applicable in the region below hadron resonances, k'² < MJ/ψ² and k² < Mφ². We report that factorizable and nonfactorizable charm contributions to the Bₛ→γ l⁺l⁻ amplitude have opposite signs. To compare the charm and the top contributions, it is convenient to express the NF charming loop contribution as a non-universal (i.e., dependent on the reaction) q²-dependent correction ΔNFC₇(q²) to the Wilson coefficient C₇. For the Bₛ→γ l⁺l⁻ amplitude, the correction is found to be positive, ΔNF C₇(q²)/C₇ > 0.